Electrodeposition of films of particles on cathodes

ABSTRACT

Films of discrete fine particles of inorganic and organic materials can be cathodically electrodeposited at low voltages from aqueous solutions of salts of non-plating monovalent cations such as solutions of sodium sulfate. For example, particles such as barium sulfate, boron and polyvinyl chloride can be deposited on a cathode from solutions of sodium sulfate in which the particles are dispersed. These films of particles can be used as such or can then be rinsed and transferred to plating baths and the films of particles can thus be imbedded in a metal matrix. Such 2-phase composite plates can be used for engineering purposes such as anti-friction applications, and the like, or with multiple plates to obtain excellent protection against atmospheric corrosion.

United States Patent [191 Brown et al.

[ 1 ELECTRODEPOSITION OF FILMS OF PARTICLES ON CATI-IODES [75]Inventors: Henry Brown, Sarasota, Fla;

Thaddeus W. Tomaszewski, Dearborn, Mich.

[22] Filed: June 26, 1972 [21] Appl. No.: 266,102

Related US. Application Data [62] Division of Ser. No. 834,901, June 19,1969, Pat. No.

[58] Field of Search 204/181, 52 R; 106/286; 260/296 F, 29.6 R, 29.2 N

[56] 1 References Cited UNITED STATES PATENTS 3,046,147 7/1962 Hathawayet al. 106/286 3,089,780 5/1963 Siple 106/286 3,619,355

1-1/1971 Silberman 106/286 Nov. 18, 1975 3,672,970 6/1972 Tomaszewski204/52 R 3,692,727 9/1972 Peschko 260/296 F OTHER PUBLICATIONSKirk-Othmer, Encyclopedia of Chem. Technology, Vo1. 8,(1965)PP. 27, 30and 31.

Primary Examiner-Allan Lieberman Attorney, Agent, or Firm-B. F. Claeboe[57] ABSTRACT Films of discrete fine particles of inorganic and organicmaterials can be cathodically electrodeposited at low voltages fromaqueous solutions of salts of nonplating monovalent cations such assolutions of sodium sulfate. For example, particles such as bariumsulfate, boron and polyvinyl chloride can be deposited on a cathode fromsolutions of sodium sulfate in which the particles are dispersed. Thesefilms of particles can be used as such or can then be rinsed andtransferred to plating baths and the films of particles can thus beimbedded in a metal matrix. Such 2-phase composite plates can be usedfor engineering purposes such as anti-friction applications, and thelike, or with multiple plates to obtain excellent protection againstatmospheric corrosion.

8 Claims, No Drawings ELECTRODEPOS ITION OF FILMS OF PARTICLES ONCATHODES I I This is a division of application Ser. No. 834,901, filedJune 19, 1969, now U.S. Pat. Ser. No; 3,687,824.

This invention relates to the Cathodic electrodeposition of finebath-insoluble particles dispersed in'aqueous electrolytes comprisingwater-soluble salts v of monovalent cations, such as sodium sulfate,potassium sulfate, lithium sulfate and the like, which do not yield, onsolid cathodes, electrodeposits of the monovalent cation from aqueoussolutions.

It has now been found that if fine bath-insoluble par ticles or powderssuch as those of barium sulfate, aluminum oxide, silicon carbide,aluminum silicate molybdenum sulfide, graphite, boron, silicon, silicondioxide, glass, aluminum, zirconium silicate, polyvinyl chloride,polyvinylidene chloride, fluorocarbon resins such aspolytetrafluoroethylene, polyamides, polyethylene and the like, aredispersed in aqueous solutions of salts of monovalent cations such asalkali metal or ammonium sulfate solutions, they can be electrodepositedon cathods using the similar low voltages and the current densitiesemployed in the electroplating of metals from aqueous solutions, as innickel plating from Watts baths.

The adherence of the particles to clean steel, brass,

copper, nickel, stainless steel or the like, cathodes is surprising. Thefilms of deposited particles can be rinsed in fast flowing water withoutloss of the film of particles. The films can be dried at 110C forseveral hours and not lose their adherence. The films can, however, berubbed off with a brush or a cloth. Nevertheless, the importance of thismethod to produce films of particles on metal lies in the fact thatthese films do have sufficient adherence that they can be furtherprocessed after rinsing-or drying of the articles with theelectrodeposited films of particles remaining substantially intact. Forexample, if fine barium sulfate or strontium sulfate powders or mixturesare deposited on a nickel surface and then this surface is given a thinplate, 0.005 to 0.05 mil of chromium, silver, gold, rhodium, a beautifulsatin or lustrous satin final finish can be obtained which will haveremarkable resistance to corrosion in industrial and marine atmospheres.The reason for this, is that the final plates of chromium or gold, etc.will be microporous because of the presence in the underlyingplate ofthe imbedded fine particles.

The microporosity of the final more noble metal causes a very markeddecrease in the anodic current density in .the pores of the final plate,thus greatly decreasing the rate of corrosion pitting.

It is also possible to transfer the cathodes with the electrodepositedfilms of particles to electroless (electrodeless) copper or nickel orcobalt (or the alloys ofthe iron group) plating baths, and thus imbedthe films of particles inelectroless copper, nickel, cobalt or thealloys of these metals. In the case of nickel-phosphorous ornickel-boronalloys obtained by these electroless processes, the introduction offine,-inorganic particles into the matrix of these alloys tends tofurther harden the plate which is important for wear resistanceproblems.

If ductile metals are deposited films of organic thermoplastic particlessuch as polystyrene which can be vaporized or. dissolved out, not onlycan porous foil be made, but with thicker plate, foils could be obtainedwith only one side porous, which would help, for example, in makingstrong laminates to plastic surfaces. Also duplex foils can be made byplating over a film of deare particles that settle in the bath andsufficient agitation of the solution must be used to maintain 'the particles in suspension in the bath. This is unlike the electrophoreti'cdeposition of organic resin particles either from monomeriform or fromcolloidal polymer form. In these cases, the organic resin particlesdeposit on anodes, an d in colloidal form do not require agitation tomaintain their suspension in the bath.

The operating baths of the present invention are aqueoussolutionscontaining monovalent cations, such as alkali metal andammonium cations. The alkali metal monovalent cations and the ammoniumcation may be used as sulfate salts such as ammonium sulfate, as carsuchas sodium methyl or ethyl sufonates, sodium benz'ene sulfonate, sodiumnaphthalene trisulfonate, and 'the like. The preferred operating pH isfrom about 4 to 10.5, as higher, and especially lower pH values tend toyield thinner films of most of'the fine particlessuspended in the baths.Mixed salts may be used. The lower concentration values-of the salts,such as 30 to 100 grams/liter are preferred over the higherconcentrations to obtain the best deposition rates. The temperatureofthe baths is not critical and deposition rates of the powders are justas good at C or higher, as at room temperature or lower.

In general, surfactants such as sodium 2-ethyl hexyl sulfate and sodiumn-octyl sulfate may be usedin the baths, even non-ionic and cationic orionically neutral sulfobetaines may be used. Buffers such as boric aciddecrease the rate of deposition of the particles, and as mentioned,[excellent results are, obtained from the simple baths consisting ofsodium, potassium, lithium, or ammonium,'rubidium and'cesium sulfates.Amine sulfates may also be used but the preferred salts are in generalsodium and potassium, lithium and ammonium sulfates or mixtures of thesesalts.

Various particles or powders may be incorporated in the baths forplating onto the cathode surfaces. For example, if in a plainair-agitated 100 g/l sodium sulfate solution there is dispersed 25-150g/l of barium sulfate powder of 0.05 to 5 microns particle size, or 5-50g/l of fine boron'powder of similar particle size, or silicon carbidepowderof 0.1 to 7 microns particle size, in concentrations ofabout 1 to100 g/l, or of 0.01 to 5 mifound that a film of eachof these particlescan be deposited within a few minutes on a cathode using currentdensities of about 5 to amps/ sq. ft. Air agitation or mechanicalagitation keeps the particles quite uniformly dispersed in, the bath.With the sulfate electrolyte, the anodes may be graphite, lead or nickelor other insoluble electrodes in aqueous sulfate solutions and as hasbeen noted the temperature of the bath can be from room or lower to atleast 60C. I

, Other very useful examples of the process and method of this inventionare thermoplastic resin parti cles such as polyvinylidene chloride, PVC,polyethylene, polyamides and polytetrafluoroethylenes plated out as afilm of dense discrete particles can be heated to form a continuousfilm. With polytetrafluoroethylene and other fluorocarbon resin powders,the addition ofa fluorocarbon surfactant to the aqueous bath helps toobtain maximum deposition of dense films of the particles. PVC,polyethylene and polyvinylidene chloride are deposited very readily andgood continuous films can be formed by heating the films. Anotherimportant example is glass and ceramic films by heat treatment ofarticles coated with electrodeposits of fine glass and ceramicparticles. Still another important example, is the electrodeposition ofboron powder or silicon powder on stainless steel or nickel or monelcathodes. The films of boron powder or silicon powder can then act as aflux in the joining of stainless to stainless, or stainless to nickel,or the like, by pressing, for example, boron powder filmed stainlessarticle to another stainless or nickel article and heating to a hightemperature in a vacuum. Mixed particles, such as barium sulfate andPVC, barium sulfate and graphite, and the like may also be used. lNorder that those skilled in the art may better understand the presentinvention and the manner in which it may be practiced, the followingspecific examples are given. These are merely exemplary of the presentinvention and the manner in which it may be practiced and are not to betaken as a limitation thereof.

EXAMPLE 1 Plating baths containing the following components, in theamounts indicated are formulated and operated under the conditions asset forth:

Concentration in Grams per Liter Na,SO .l H O I00 250 BaSO fine powder(0.l to 3 microns particle size) 1 I50 Nickel plated cathode Graphiteanode Air agitation Room Temperature Cathode current density 5 I00amps/sq. ft. Plating time 1 l0 minutes A film of barium sulfateparticles is deposited over the entire cathode. After rinsing, thenickel plated cathode with its film of fine barium sulfate istransferred to a chromium plating bath and plated with 0.005 to 0.02 milof chromium, or similar thicknesses of gold plate from an alkaline oracidic gold plating bath. A beautiful satin appearance is obtained ineach case. The corrosion protection for the underlying basis metal ofsteel or zinc die cast that is copper plated, then nickel plated beforeelectrodepositing the film of fine particles and then the final platingwith chromium or gold, or for that matter silver or rhodium, is trulyoutstanding. Corrodkote and CASS accelerated tests show the extremelyexcellent corrosion protection obatined, compared to the case wherethere is no film of particles present. The film of particles can beplated with thin nickel prior to the chromium, gold, silver or rhodiumfinal plate.

EXAMPLE 2 Instead of barium sulfate particles in the same bath as inExample 1, precipitated silica particles or micronized silica hydrogelsof ultimate particle size of about 0.01 to 0.03 micron are used inconcentrations of 5 to 50 g/l, and when the same plating tests are run,the same excellent results are obatined except that the appearance ofthe final thin chromium or gold or silver of rhodium plate is as brightor almost as bright as the underneath nickel. That is, when the ultimateparticle size of the silica particles is around 0.02 micron, even thoughagglomerate sizes may be as large as 6 to 10 microns, the particles donot cause appreciable dulling of the subsequent plate. In the same wayaluminum silicate, zirconium silicate, zirconium oxide, are depositedand then covered with a subsequent thin plate of nickel and followed bychromium or gold, etc., or directly by a thin plate of chromium, gold,silver, rhodium, tinnickel alloy plate and obtain a composite plate ofgreatly improved corrosion protection to the underlying metal. If thenickel plate on the basis metal was freshly deposited and is not rinsedperfectly, the drag-in of nickel plating salts into the sodium sulfateor potassium or lithium sulfate or chloride solutions will cause noproblems in the deposition of the powders. With chloride baths such assodium chloride and potassium chloride, chlorine will be evolved atinsoluble anodes such as graphite and for this reason chlorideelectrolytes are not as generally preferred.

EXAMPLE 3 Instead of fine powders of silica, barium sulfate, aluminumsilicate and zirconium oxide eletrodeposited and processed as describedin Example 2, films of fine powders of molybdenum sulfide, graphite,lead powder or mixtures are electrodeposited as films on a metal such assteel, aluminum, copper, nickel, bronze, brass, etc. and subsequentlyplated with thin plates of copper, nickel, silver, bronze, brass, tin,lead, lead-tin alloy and lead-tin-copper alloy. Multiple layers are alsoplated such as a thin plate of copper followed by a thin film of tin andthen heat diffused to obtain a bronze matrix with imbedded particles oflead or graphite or molybdenum sulfide or mixtures. Additionally, alead-tin plate (90l0) can also be plated over the copper or nickelplate. Such surfaces make excellent bearing surfaces of low friction andanti-seizing properties and are excellent for cold starting.

EXAMPLE 4 Following the procedure of the proceeding examples, thepowders are electrodeposited on a passive surface such as dry nickelplate or a chromate dipped and rinsed nickel plate, or a stainless steelsurface or on a thin film of cadmium plate from an alkaline cyanide bathdeposited on steel on which the adhesion is poor.

. Then after a subsequent deposit of nickel, iron, cobalt EXAMPLE 5Fluorocarbon particles are cathodically deposited on a metal orconducting surface with the following bath.

Concentration in Grams per Liter Na SO. or K 80 10 100 amps/sq. n.Graphite anode Cathode current density Room Temperature to 60C Airagitation Plating time I l5 minutes After depositing a film offlurorocarbon particles, a

thin copper, brass, bronze, silver, lead-tin, lead-tin-copper alloy ornickel plate less than about 1 mil is deposited over the particles andan excellent anti-friction bearing surface is obtained. Where nickel isused with a final thin chromium plate, excellent corrosion protectionfor the basis metal is obtained. Foils are obtained when plated on apassive surface as previously described in Example 4. Where the foilsare thick, over about 1 mil, then one side will contain the denselydeposited particles and the final plated side will be free of particles.

What is claimed is:

l. A bath for cathodically electrodepositing films of fine particles,which comprises at least one waterinsoluble powder having a particlesize in the range of from about 0.01 to 10 microns and being present inamount ranging from about 1 to 150 g/l dispersed in a aqueous solutionof about 30 to about g/l of salts of monovalent cations selected fromthe class of the alkali metal cations and the ammonium cation, saidsolution being free of ions that can be electroplated.

2. A bath in accordance with claim 1, wherein said monovalent cationsare present in the aqueous solution as sulfate salts.

3. A bath in accordance with claim 1, wherein said water-insolubleparticles are barium sulfate particles.

4. A bath in accordance with claim 1, wherein said water-insolubleparticles are boron particles.

5. A bath in accordance with claim 1, wherein said water-insolubleparticles are silicon particles.

6. A bath in accordance with claim 1, wherein said water-insolubleparticles are silicon carbide particles.

7. A bath in accordance with claim 1, wherein said monovalent cationsare present in the aqueous solution as carbonates.

8. A bath in accordance with claim 1, wherein said monovalent cationsare present in the aqueous solution as sulfonate.

1. A BATH FOR CATHODICALLY ELECTRODEPOSITING FILMS OF FINE PARTICLES,WHICH COMPRISES AT LEAST ONE WATER-INSOLUBLE POWDER HAVING A PARTICLESIZE IN THE RANGE OF FROM ABOUT 0.01 TO 10 MICRONS AND BEING PRESENT INAMOUNT RANGING FROM ABOUT 1 TO 150 G L DISPERSED IN A AQUEOUS SOLUTIONOF ABOUT 30 TO ABOUT 100 G L OF SALTS OF MONOVALENT CATIONS SELECTEDFROM THE CLASS OF THE ALKALI METAL CATIONS AND THE AMMONIUM CATION, SAIDSOLUTION BEING FREE OF IRONS THAT CAN BE ELECTROPLATED.
 2. A bath inaccordance with claim 1, wherein said monovalent cations are present inthe aqueous solution as sulfate salts.
 3. A bath in accordance withclaim 1, wherein said water-insoluble particles are barium sulfateparticles.
 4. A bath in accordance with claim 1, wherein saidwater-insoluble particles are boron particles.
 5. A bath in accordancewith claim 1, wherein said water-insoluble particles are siliconparticles.
 6. A bath in accordance with claim 1, wherein saidwater-insoluble particles are silicon carbide particles.
 7. A bath inaccordance with claim 1, wherein said monovalent cations are present inthe aqueous solution as carbonates.
 8. A bath in accordance with claim1, wherein said monovalent cations are present in the aqueous solutionas sulfonate.